1. Field of the Invention
The invention relates to communication systems, and more particularly to multi-carrier communication systems.
2. Description of the Related Art
A multi-carrier communication system uses a plurality of carriers for signal transmission. The multiple carriers of the multi-carrier communication system are divided into fully configured carriers and partially configured carriers. A fully configured carrier carries complete system information. A partially configured carrier carries only partial system information. Referring to FIG. 1, a schematic diagram of a multi-carrier communication system is shown. In one embodiment, the multi-carrier communication system comprises a base station 102 and a mobile station 104. The base station 102 broadcasts signals via a plurality of fully configured carriers 1˜M and a plurality of partially configured carriers 1˜N.
When the mobile station 104 tries to access data of the multi-carrier communication system, because the partially configured carriers 1˜N do not comprise complete network entry information, the mobile station 104 cannot directly access data via the partially configured carrier 1˜N. On the contrary, the mobile station 104 must first accesses the fully configured carriers 1˜M, and then obtain network entry information from one of the fully configured carriers 1˜M, and then access data from the partially configured carriers 1˜N according to the network entry information obtained from the fully configured carriers. Thus, to reduce network entry latency, the mobile station 104 must identify which one of the multiple carriers of the multi-carrier communication system is a fully configured carrier. Otherwise, if the mobile station 104 cannot identify whether a carrier is a fully configured carrier, when the mobile station 104 starts to enter the network of the multi-carrier communication system, the mobile station 104 spends a lot of time in accessing the partially configured carriers, while not obtaining information required for network entry; thus, resulting in a long network entry latency.
Preambles of a carrier comprise a lot of information for accessing the carrier. Preambles are divided into primary preambles and secondary preambles. A primary preamble may carry information about carrier bandwidth, sector number, type of a base station, and partial cell ID. A secondary preamble may carry cell ID information or partial cell ID information. A mobile station uses a primary preamble for symbol boundary detection, and a mobile station may use a secondary preamble as an indicator for radio signal strength.
The fully configured carriers 1˜M and the partially configured carriers 1˜N of a conventional multi-carrier communication system both have hierarchical preamble designs. Referring to FIG. 2, a schematic diagram of hierarchical preambles of a fully configured carrier and a partially configured carrier of a conventional multi-carrier communication system is shown. In one embodiment, each frame of the fully configured carrier comprises a primary preamble 202 and three secondary preambles 204, 206, and 208. In one embodiment, each frame of the partially configured carrier comprises a primary preamble 212 and three secondary preambles 214, 216, and 218. Thus, the fully configured carrier and the partially configured carrier have the same hierarchical preamble designs, and the mobile station 104 cannot differentiate the fully configured carrier from the partially configured carrier according to the preambles thereof.
Because preamble detection is a first step in a network entry procedure, if a mobile station can identify whether a carrier is a fully configured carrier or a partially configured carrier according to the preambles of the carrier, the mobile station can obtain network entry information from a fully configured carrier as soon as possible; thereby reducing network entry latency to improve performance of the mobile station. Thus, a new multi-carrier communication system comprising partially configured carriers with different preamble designs from those of fully configured carriers are provided.